B16a2 engine work

It’s got a custom air intake, exhaust manifold and exhaust and every piece of adjustable suspension you can buy

Gearbox is an s4c with a mfactory metal plate lsd and 4.9 final drive

Cars fully stripped and only used for track days but looking to get into racing

My question is.... is it worth modifying the engine without spending mega bucks, say skunk 2 tuner 2 cams, valve springs and retainers? Maybe port the head? Would it be worth the gains or would I be better off spending the money elsewhere

Well, if it's an N/A build then by all means, please go ahead, I am thinking of getting a B20b bottom end, B16B pistons, B18C cams, adjustable cam gears, and shaving my B16A head.
Why are you wanting to do this? Is it to improve the lap times? Or just so you can say you have them in the engine? It is a lot of money, and to be honest, it may not be worth it in the long run... I have heard people losing BHP on SKUNK2 tuner cams. Personally, I'd get some B16b or B18C cams, you don't need to change the retainers if you have a raised rev limiter. Can't see any harm if you didn't use the B18C retainers and valve springs.